Wiring substrate, electronic device, and electronic module

ABSTRACT

A wiring substrate includes an insulating substrate, a conductor layer and an interlayer. The insulating substrate contains AlN. The conductor layer contains Cu. The interlayer is located between the insulating substrate and the conductor layer. In the interlayer, between a first region near the insulating substrate and a second region near the conductor layer, Cu concentration is higher in the second region than in the first region, and Al concentration is higher in the first region than in the second region.

TECHNICAL FIELD

The present disclosure relates to a wiring substrate, an electronicdevice and an electronic module.

BACKGROUND

In JPH 5-182926 A, there is disclosed a manufacturing method of a wiringsubstrate in which an Al (aluminum)-based wiring is disposed on asubstrate with a barrier metal layer in between. In this manufacturingmethod, after a small-diameter connecting hole is formed in the surfaceof the substrate, the barrier metal layer and the wiring layer aresuccessively formed by sputtering. As the barrier metal layer, aTi-based material is used.

SUMMARY

A wiring substrate according to the present disclosure includes:

an insulating substrate containing AlN;

a conductor layer containing Cu; and

an interlayer located between the insulating substrate and the conductorlayer,

wherein in the interlayer, between a first region near the insulatingsubstrate and a second region near the conductor layer,

-   -   Cu concentration is higher in the second region than in the        first region, and    -   Al concentration is higher in the first region than in the        second region.

An electronic device according to the present disclosure includes:

the above wiring substrate; and

an electronic component mounted on the wiring substrate.

An electronic module according to the present disclosure includes:

the above electronic device; and

a module board where the electronic device is mounted.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A shows a wiring substrate according to an embodiment of thepresent disclosure.

FIG. 1B is a part-enlarged view of a part of the wiring substrate shownin FIG. 1A.

FIG. 1C shows an electronic module according to the embodiment of thepresent disclosure.

FIG. 2A shows concentration distributions of constituent elements in andaround an interlayer of the wiring substrate of the embodiment.

FIG. 2B shows concentration distributions of the constituent elements inand around an interlayer of a comparative example.

FIG. 3 is a sectional view of structure at and around an interface of aninsulating substrate.

FIG. 4 shows concentration distributions of constituent elements in andaround the interface in a recess.

FIG. 5 is a diagram to explain an example of a manufacturing method ofthe wiring substrate of the embodiment.

DETAILED DESCRIPTION

Hereinafter, an embodiment(s) of the present disclosure will bedescribed in detail with reference to the drawings.

FIG. 1A is a sectional view of a wiring substrate according to anembodiment of the present disclosure. FIG. 1B is a part-enlarged view ofa part of the wiring substrate shown in FIG. 1A. FIG. 1C is a sectionalview of an electronic module according to the embodiment of the presentdisclosure.

A wiring substrate 10 of this embodiment has an insulating substrate 12and a conductor layer 14 formed on the plate surface of the insulatingsubstrate 12. The conductor layer 14 is formed with a pattern on theinsulating substrate 12, and functions as a wiring for transmittingsignals or electric power or functions as an electrode or a connectionpad for connecting an electronic component 20, such as an opticalelement. In the insulating substrate 12 and on the back surface of theinsulating substrate 12 (on a side thereof opposite the conductor layer14), a wiring(s) and/or a connection pad(s) 31 (FIG. 1C) may also beprovided. The wiring substrate 10 may be a package having a recess wherethe electronic component 20 is housed.

An electronic device 40 of this embodiment is, as shown in FIG. 1C,configured by mounting the electronic component 20 on the wiringsubstrate 10 shown in FIG. 1A. The electronic component 20 is mountedsuch that a terminal of the electronic component 20 is electricallyconnected to the conductor layer 14. The connection form of the terminalof the electronic component 20 to the conductor layer 14 may be anyform, examples of which include connection with a joining material, suchas solder, and connection by wire bonding. In FIG. 1C, the electroniccomponent 20 is mounted on the conductor layer 14, but may be mounted,of the wiring substrate 10, a portion where the conductor layer 14 isnot present. As the electronic component 20, various electroniccomponents are applicable, which include: optical elements, such as anLD (Laser Diode), a PD (Photo Diode) and an LED (Light Emitting Diode);imagers, such as a CCD (Charge Coupled Device) and a CMOS (ComplementaryMetal Oxide Semiconductor) device; piezoelectric vibrators, such as acrystal oscillator; surface acoustic wave devices; semiconductordevices, such as a semiconductor integrated circuit (IC) device;electric capacitors; inductors; and resistors.

An electronic module 100 of this embodiment is, as shown in FIG. 1C,configured by mounting the electronic device 40 on a module board 110.On the module board 110, in addition to the electronic device 40, otherelectronic component(s) and/or electric component(s) may be mounted. Themodule board 110 has a circuit wiring and a connection pad 111 thatconnects components. The electronic device 40 can be mounted on themodule board 110, for example, via (with) a joining material 113, suchas solder.

<Wiring Substrate>

The insulating substrate 12 of the wiring substrate 10 contains AlN(aluminum nitride) as a main component of constituent elements. Theconductor layer 14 contains Cu (copper) as a constituent element. At theinterface between the insulating substrate 12 and the conductor layer14, an interlayer 16 is present. The interlayer 16 has a thickness ofabout 20 nm to 80 nm.

FIG. 2A shows concentration distributions of constituent elements in andaround the interlayer of the wiring substrate of the embodiment. FIG. 2Bshows concentration distributions of the constituent elements in andaround an interlayer of a comparative example. The constituent elementsof the interlayer 16 and the concentration distributions of theconstituent elements in the interlayer 16 described hereinafter wereobtained by measurement with TEM-EELS (Electron Energy-LossSpectroscopy). The concentration distributions are expressed byconcentrations with at % (atomic percent). The graphs shown in FIG. 2Aand FIG. 2B do not show values of the concentration distributionsprecisely, but show changes of the values in a simplified manner.

As shown in FIG. 2A, the interlayer 16 contains Al (aluminum), N(nitrogen) and Cu (copper). If, among regions of the interlayer 16, afirst region 16 r 1 near the insulating substrate 12 is compared with asecond region 16 r 2 near the conductor layer 14, Cu concentration ishigher in the second region 16 r 2 than in the first region 16 r 1.Further, Al concentration is higher in the first region 16 r 1 than inthe second region 16 r 2. Still further, N concentration may be higherin the first region 16 r 1 than in the second region 16 r 2. In theinterlayer 16, The Al and N concentrations may gradually decrease in adirection from the insulating substrate 12 to the conductor layer 14.The first region 16 r 1 and the second region 16 r 2 are two regionsthat do not overlap one another and have an arbitrary thickness (e.g. athickness of 10% of the interlayer 16) in the layer direction. The firstregion 16 r 1 may be a region closer to the insulating substrate 12 thanthe second region 16 r 2 is, and the second region 16 r 2 may be aregion closer to the conductor layer 14 than the first region 16 r 1 is.Alternatively, the first region 16 r 1 may be a region closer to theinsulating substrate 12 than to the center of the interlayer 16, and thesecond region 16 r 2 may be a region closer to the conductor layer 14than to the center of the interlayer 16.

The constituent elements of the interlayer 16 may have the followingconcentration distributions, to be more specific. That is, Al and Nconcentration gradients are each a gradient in which the closer theposition in the interlayer 16 is to the conductor layer 14, the lowerthe concentration is, and Cu concentration gradient is a gradient inwhich the closer the position in the interlayer 16 is to the conductorlayer 14, the higher the concentration is. These concentration gradientsmay exist from the conductor layer 14 side to the insulating substrate12 side of the interlayer 16.

The interlayer 16 may further contain C (carbon). If the interlayer 16contains C, however, C concentration of the interlayer 16 is 10 at % orless. The conductor layer 14 may further contain C the same as theinterlayer 16. C concentration of the conductor layer 14 may be 10 at %or less the same as C concentration of the interlayer 16.

FIG. 2B, which shows the comparative example, shows the concentrationdistributions of the constituent elements of the interface not subjectedto sintering under predetermined conditions described below. In thecomparative example, changes of the concentrations of the constituentelements (Al, N, Cu) are steep on an insulating substrate 212 side of aninterlayer 216 and on a conductor layer 214 side of the interlayer 216.

Further, the interlayer 216 of the comparative example has high Cconcentrations and has a portion(s) containing C at a concentrationequal to or more than the sum of the Al, N and Cu concentrations, forexample. If the conductor layer 214 is generated by plating, carboncomponent contained in the plating solution gets mixed in the interlayer216, and the interlayer 216, which is not subjected to the sinteringunder predetermined conditions described below, has high Cconcentrations.

<Adhesive Component>

FIG. 3 is a sectional view of structure at and around an interface of aninsulating substrate.

The insulating substrate 12 has a large number of fine recesses 12D,each of which is as shown in FIG. 3, at the interface between itself andthe conductor layer 14. The constituent element(s) of the conductorlayer 14 enters each recess 12D, and the interlayer 16 is formed betweenthe insulating substrate 12 and the conductor layer 14 not only at theinterface of the region outside the recess 12D but also on the innersurface of the recess 12D. The element components and the concentrationdistributions of the interlayer 16 are as described with reference toFIG. 2A.

On the inner surface of the recess 12D, adhesive regions el containingTiO₂ (titanium oxide) as a constituent element are scattered. Theadhesive regions el may also be scattered at the interface between theinsulating substrate 12 and the conductor layer 14 of the region outsidethe recess 12D. The “scattered” means that at the interface between theinsulating substrate 12 and the conductor layer 14, the adhesiveregion(s) el and region(s) other than the adhesive region(s) el coexist.

Next, an interlayer 16A at a portion including the adhesive region elwill be described. The interlayer 16A at the portion including theadhesive region el and the interlayer 16 at a portion not including theadhesive region el are distinguished from one another by these differentreference signs. FIG. 4 shows concentration distributions of constituentelements in and around the interface including the adhesive region(s) elin a recess. The graph shown in FIG. 4 does not show values of theconcentration distributions precisely, but show changes of the values ina simplified manner.

The interlayer 16A contains Al, N, Cu, Ti (titanium) and O (oxygen). Inthe interlayer 16A too, Al, N and Cu concentration gradients in whichAl, N and Cu concentrations gradually change exist. Directions of theAl, N and Cu concentration gradients are the same as those of the Al, Nand Cu concentration gradients in the interlayer 16 described above. TheAl, N and Cu concentration gradients exist from the insulating substrate12 side to the conductor layer 14 side of the interlayer 16A. In theinterlayer 16A too, the C concentration is 10 at % or less.

Since the interlayer 16A contains Ti and O too, counter diffusion of Cuand Al is promoted in the sintering under predetermined conditionsdescribed below. Hence, the Al, N and Cu concentration gradients in theinterlayer 16A are gentle as compared with those in the interlayer 16 atthe portion not including the adhesive region el.

Further, in the interlayer 16A including the adhesive region el, O(oxygen) concentration gradient occurs on the conductor layer 14 side,so that adhesive strength of the conductor layer 14 is increased.Increase of the adhesive strength between the insulating substrate 12and the conductor layer 14 in the recess 12D further increases theadhesive strength between the insulating substrate 12 and the conductorlayer 14 as a whole.

<Adhesive Strength>

A test was carried out to obtain the adhesive strength between theconductor layer 14 and the insulating substrate 12 about the wiringsubstrate 10 of the embodiment and a board not subjected to thesintering under predetermined conditions described below. As the testmethod, to a first jig fixed to the insulating substrate 12 and a secondjig fixed to the conductor layer 14, pull force in a direction toseparate these from one another in a direction perpendicular to theinterface was applied, and the maximum pull strength was measured as theadhesive strength. As the pull force is increased, the interface betweenthe insulating substrate 12 and the conductor layer 14 fractures, or theinsulating substrate 12 fractures. As a fracture mode, a proportion offracture of the insulating substrate 12 was obtained.

Three objects were tested, which were a board not subjected tosintering, a board subjected to sintering under conditions differentfrom predetermined conditions described below, and the wiring substrate10 of the embodiment subjected to the sintering under predeterminedconditions described below and having the interface where the adhesiveregions el were scattered.

As a result of the test, as shown in the following comparison table, agreat improvement was observed in the adhesive strength of the wiringsubstrate 10 of the embodiment.

TABLE I [COMPARISON TABLE] ADHESIVE STRENGTH TREATMENT FRACTURE MODE[kgf/mm²] NO SINTERING FRACTURE OF INSULATING 2.59 SUBSTRATE: 0%DIFFERENT FRACTURE OF INSULATING 3.79 SINTERING SUBSTRATE: 20% SINTERINGUNDER FRACTURE OF INSULATING 5.83 BELOW-DESCRIBED SUBSTRATE: 100%PREDETERMINED CONDUCTIONS

<Manufacturing Method>

FIG. 5 is a diagram to explain an example of a manufacturing method ofthe wiring substrate of the embodiment.

The manufacturing method of the embodiment includes, in chronologicalorder, a pretreatment step J1 of cleaning and drying an AlN substrate70, a step J2 of applying an organic Ti solution 71 to the AlN substrate70, and a baking step J3 of baking the AlN substrate 70 to which theorganic Ti solution 71 has been applied. In the pretreatment step J1,anisotropic etching using an agent or reactive ions may be performed toform the fine recesses 12D in the surface of the AlN substrate 70. Inthe baking step J3, baking is performed under conditions of 400° C. orhigher and 30 minutes or longer. Thus, the organic Ti solution 71solidifies and becomes a titanium oxide layer 71A. This manufacturingmethod further includes a step J4 of applying electroless Cu plating 74to a substrate 72 after the baking and cooling, and a sintering step J5of performing sintering thereon.

In this manufacturing method, since the titanium oxide and the conductorlayer 14 are formed by the applying, baking and plating, the wiringsubstrate 10 can be manufactured at low cost.

In the sintering step J5, in an atmosphere of an inert gas, sintering isperformed under conditions of 300° C. or higher and 30 minutes orlonger. Through the sintering under these conditions, Cu of theelectroless Cu plating 74 reaches the AlN substrate 70 through thetitanium oxide layer 71A, so that at the interface, the interlayer 16having Al, N and Cu concentration gradients is formed.

Further, through the sintering under the conditions, C (carbon)component of the interlayer 16 diffuses from the interface to theelectroless Cu plating 74 side. In addition, through the sintering underthe conditions, the C component of the electroless Cu plating 74 reactswith O (oxygen) component contained in the plating solution, anddisperses to the outside as CO gas or CO₂ gas. Thus, C concentration ofthe interlayer 16 decreases to 10 at % or less.

Further, through the sintering under the conditions, the titanium oxidelayer 71A changes to the adhesive regions el scattered at the interface,and at the position of each adhesive region el, the interlayer 16Acontaining Ti and O is formed.

As described above, according to the wiring substrate 10 of thisembodiment, if, of the interlayer 16, the first region 16 r 1 near theinsulating substrate 12 and the second region 16 r 2 near the conductorlayer 14 are compared with one another, the Cu concentration is higherin the second region 16 r 2 than in the first region 16 r 1. Further,the Al concentration is higher in the first region 16 r 1 than in thesecond region 16 r 2. Due to these concentration gradients, from theinsulating substrate 12 side to the conductor layer 14 side of theinterlayer 16, change in coefficient of thermal expansion is gentle.This can reduce stress concentration due to difference in coefficient ofthermal expansion between films, and achieve high adhesive strengthbetween the insulating substrate 12 and the conductor layer 14.

Further, in the interlayer 16, the N concentration is higher in thefirst region 16 r 1 near the insulating substrate 12 than in the secondregion 16 r 2 near the conductor layer 14. Hence, change in coefficientof thermal expansion in the interlayer 16 is gentler. This can furtherreduce stress concentration due to difference in coefficient of thermalexpansion between films, and achieve higher adhesive strength betweenthe insulating substrate 12 and the conductor layer 14. Similarly, inthe interlayer 16, the AL and N concentrations gradually decrease in thedirection from the insulating substrate 12 to the conductor layer 14.Hence, change in coefficient of thermal expansion in the interlayer 16is gentler. This can further reduce stress concentration due todifference in coefficient of thermal expansion between films, andachieve higher adhesive strength between the insulating substrate 12 andthe conductor layer 14.

Further, according to the wiring substrate 10 of this embodiment, at theinterface of the region outside the fine recesses 12D of the insulatingsubstrate 12 and on the inner surfaces of the recesses 12D, theinterlayer(s) 16 having Al, N and Cu concentration gradients is present.This can achieve higher adhesive strength between the insulatingsubstrate 12 and the conductor layer 14.

Further, according to the wiring substrate 10 of this embodiment, on theinner surfaces of the recesses 12D, the interlayer(s) 16A containing Tiand O is scattered. Ti and O forming no layer but being scattered canachieve gentler Al, N and Cu concentration gradients at portions wherethe interlayer 16A containing Ti and O is scattered and therearound, andaccordingly achieve higher adhesive strength of the interface. Further,achieving higher adhesive strength inside the recesses 12D can furtherincrease the adhesive strength between the insulating substrate 12 andthe conductor layer 14 as a whole.

Further, according to the wiring substrate 10 of this embodiment, in theinterlayers 16, 16A, the C concentration is 10 at % or less. If Coccupies an interface, strength of the interface decreases. In thisembodiment, decrease of the strength due to C of the interface issuppressed. The structural element having the above C concentration andits effect are especially effective if the conductor layer 14 is formedby plating.

Further, according to the electronic device 40 and the electronic module100 of this embodiment, the wiring substrate 10 in which the adhesivestrength of the conductor layer 14 is high is used. This exhibits aneffect of achieving high reliability.

In the above, an embodiment(s) of the present disclosure has beendescribed. However, the present disclosure is not limited to the aboveembodiment. For example, in the above embodiment, at the interfacebetween the insulating substrate 12 and the conductor layer 14, theadhesive regions containing Ti and O are scattered, but this structuremay not be provided. Further, the C (carbon) concentration of theinterlayer may be different from that described in the above embodiment.Further, in the above embodiment, an example of the manufacturing methodof the wiring substrate has been described, but the wiring substrateaccording to the present disclosure may be manufactured by amanufacturing method different from that of the above embodiment.Further, the details described in the above embodiment can beappropriately modified within a range not departing from the scope ofthe disclosure.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to a wiring substrate, anelectronic device and an electronic module.

1. A wiring substrate comprising: an insulating substrate containingAlN; a conductor layer containing Cu; and an interlayer located betweenthe insulating substrate and the conductor layer, wherein in theinterlayer, between a first region near the insulating substrate and asecond region near the conductor layer, Cu concentration is higher inthe second region than in the first region, and Al concentration ishigher in the first region than in the second region.
 2. The wiringsubstrate according to claim 1, wherein N concentration is higher in thefirst region than in the second region.
 3. The wiring substrateaccording to claim 1, wherein in the interlayer, the Al concentrationand N concentration gradually decrease in a direction from theinsulating substrate to the conductor layer.
 4. The wiring substrateaccording to claim 1, wherein the insulating substrate has a pluralityof recesses on a conductor layer side thereof, and wherein theinterlayer is present outside the recesses and in the recesses.
 5. Thewiring substrate according to claim 4, wherein the interlayer furthercontains Ti and O.
 6. The wiring substrate according to claim 4, whereinTi of the interlayer is scattered at an interface of the insulatingsubstrate in the recesses.
 7. The wiring substrate according to claim 1,wherein from an insulating substrate side to a conductor layer side ofthe interlayer, C concentration is 10 at % or less.
 8. An electronicdevice comprising: the wiring substrate according to claim 1; and anelectronic component mounted on the wiring substrate.
 9. An electronicmodule comprising: the electronic device according to claim 8; and amodule board where the electronic device is mounted.
 10. The wiringsubstrate according to claim 2, wherein in the interlayer, the Alconcentration and N concentration gradually decrease in a direction fromthe insulating substrate to the conductor layer.
 11. The wiringsubstrate according to claim 2, wherein the insulating substrate has aplurality of recesses on a conductor layer side thereof, and wherein theinterlayer is present outside the recesses and in the recesses.
 12. Thewiring substrate according to claim 3, wherein the insulating substratehas a plurality of recesses on a conductor layer side thereof, andwherein the interlayer is present outside the recesses and in therecesses.
 13. The wiring substrate according to claim 10, wherein theinsulating substrate has a plurality of recesses on a conductor layerside thereof, and wherein the interlayer is present outside the recessesand in the recesses.